In attempting to control environmental pollution from industries, human waste, and naturally decomposing minerals and chemicals, a wide variety of chemical and mechanical processes have been developed.
Chemical methods have attempted to cause a predetermined reaction between chemical additives and impurities contained within an aqueous solution. The most common reactions are designed to cause coalescences of the impurities and the chemical additives. As the coalescing occurs the materials flocculate and the particles which are then formed layer to their specific gravity within the aqueous solution. Many times, to effectively remove the chemically flocculated contaminants, additional chemicals are added to increase the size of the particles and thus the specific gravity of the particle. Increasing the size of the floc with additional chemical additives causes more rapid settling and better defined segregated layering within the solution. Air can be added to some solutions to cause a more rapid rise of the flocculated particles when the formed particles have a lighter specific gravity than the base solution. Combinations of chemicals and air can be used for complex aqueous solutions that have more than one contaminant.
Mechanical methods are designed to achieve similar results as chemical additives, but to a lesser degree of purity in the final aqueous solution. Filters, centrifuges, plate separators, and clarifiers are the most common mechanical methods employed to remove contaminants from aqueous solutions. In most cases the impurities that are removed mechanically are suspended solids or dissolved particles that are flocculated by changes in process temperature or retention time in the processed solution.
Over two decades ago, the chemical and mechanical methods of treating the aqueous solutions were thought to be adequate treatment prior to disposal. Disposal of the treated aqueous solution into the oceans, streams, lakes, and underground wells were common. Tests have shown that small amounts of impurities that escaped treatment from chemical or mechanical process or a combination of both processes have accumulated in soils, ground waters, lakes, and river beds. Many rivers and streams are now considered to be wastesites. Lakes have been drained and their lake beds have been hauled away to be treated as hazardous waste. Many times the chemical residue left from an original reaction which was used to remove a waste from industrial aqueous solutions became the residual waste and required additional chemicals and/or processing but did not receive additional processing, and the aqueous solution was unsafely discharged to the natural environment.
Causing the coalescence of contaminants without the addition of chemicals has been successfully performed by electrolytic treatment for several years. However, the previous electrolytic processes created large quantities of metal and other contaminant sludges which added to the cost of disposal. Many current systems for performing electrolytic treatments are batch and dump methods which have a high labor cost, since each batch is individually sampled, treated, and separated prior to beginning the second batch.
On-line electrolytic systems, as opposed to batch systems, require large spaces for process retention time. Retention time is critical for the on-line system to obtain treatment standards. Retention time can be shortened with higher voltage and more electrical power consumption. On-line systems usually require a larger electrical supply, due in part to the retention time and the voltage required to electrically charge the pipe mass which is delivering the charge and transporting the liquid through the system. Capital costs are high and the cost for electrical power to operate the system is expensive. Since the required voltage and amperage across the poles is high the resulting flux is such that the piping deteriorates quickly, and maintenance for replacing the piping is frequent.
Accordingly, there is a need for an efficient, low cost liquid contaminant removal system which embodies the best of all previous systems, yet remains flexible to treat a wide variety of waste streams on-line with minimal maintenance and energy cost.